The invention pertains to a control device for the parking lock of a motor vehicle with at least one actuating drive element that can be operated by triggering means, with which at least one locking device of the parking lock can be brought from an engaged position, into which it is pressed by a retaining force, into a disengaged position.
For current vehicle transmissions (synchronized, power-shifting or automatic transmissions), the parking lock is usually set manually via a mechanical linkage in order to block the rotational motion of gear or vehicle wheels with a positive lock. As part of increasing driver comfort, transmissions have been designed with an electrically operated shifting of gears, so that the gear-shift command from the driver is done by pushing a button. It would make sense for the parking lock also to be incorporated into this servo operation. When infinitely variable transmissions, which can implement a non-positively locked stop by setting an infinitely high transmission rate, are used, the actuation of the parking lock ought to be automated so that the transition from the non-positive stop to the park position (and vice versa) takes place without interruption of the braking force of the vehicle. It is therefore sought to design the actuation of the parking lock (a mechanical, positive locking of an output-side gearwheel) such that setting and releasing the lock takes place by transmission of an electric command.
Since the operating safety of the vehicle depends quite crucially on the functioning of the parking lock, its design and layout should be operationally secure, that is, redundant. This pertains above all else to the reliable execution of the driver""s desire for locking and unlocking, the prevention of unintended locking during travel and of unintentional unlocking while stopped (due, for instance, to failure of auxiliary power, a short circuit in the power circuit and the like).
The problem underlying the invention is viewed to be the specification of a control device for the parking lock of the initially mentioned type, by which means the aforementioned requirements are met. In particular, the control device should permit safe, reliable actuation of the parking lock. It should be possible for it to be manufactured in a simple, economical manner and constructed such that it can be retrofitted into existing transmissions without significant difficulties.
According to the invention, at least two triggering means acting independently on the actuating drive element are provided, which interact with the actuating drive element such that movement of the locking device out of the engaged position into the disengaged position or, conversely, from the disengaged position into the engaged position takes place only if the two triggering means are triggered with changeover signals in the same sense.
This can be implemented in various ways. For instance, the actuating drive element can be a magnetic solenoid plunger which engages the locking device when it is de-energized and disengages it when it passes current. The triggering means can be electrical switches situated in the power circuit of the solenoid plunger and actuated by an electrical controller via electrical switching signals.
A preferred embodiment of the invention provides an electro-hydraulically operated controller. The drive element here is preferably a hydraulic actuating piston under initial spring tension, which brings the parking lock into its disengaged position upon application of pressure. The triggering means are expediently constructed as electrically triggerable hydraulic valves, which can be brought against the force of a spring by electrical signals from an idle position into an active position. 3/2-way solenoids come into particular consideration.
In this case, the hydraulic valves convert electrical commands into hydraulic commands. In particular, they are connected, in conjunction with the check valves, such that a change of state for the parking lock (unlocking or locking) takes place only if both hydraulic valves switch in the same sense. If both hydraulic valves are in the de-energized state, then the actuating drive element, specifically, the actuating piston, is connected to the non-pressurized sump and inflow from the pressure source to the sump is cut off, so that the actuating drive element, and with it the parking lock, is in the engaged, locked position. If power is applied to both hydraulic valves, their magnetic slides are pushed against the force of their respective restoring springs into the position in which the actuating drive element is connected to the pressure source and separated from the sump. Under the force of the system pressure from the pressure source, the actuating drive element moves into its disengaged, unlocked position against the force of the parking lock spring providing retaining force.
The check valves mentioned in claims 5 and 6 are connected in opposite directions and are preferably held in their closed positions by restoring springs. With a sufficiently high hydraulic pressure, the check valves can be opened against the spring force.
Independently of the state (engaged or disengaged) in which the parking lock is situated, this state is preserved if only one hydraulic valve is changed over. Such a changeover can be initiated, for instance, by an unintentional electrical signal (e.g., by an electrical short circuit to ground or to a 12-V power source).
It is expedient for a spring-loaded input check valve, which blocks flow back to the pressure source in case of loss of system pressure that may unexpectedly occur during travel and can thus preserve pressure on the actuating drive element, to be placed in the inlet path of pressure flow to the hydraulic valves. In this way, a sudden engagement of the parking lock during travel due to loss of pressure in the system (pump damage, leakage in the system, etc.) is prevented. The design can be such that the pressure in the actuating drive element can be maintained for approximately 10 min, so that time remains for the vehicle user to bring the vehicle to a controlled stop after the appearance of a warning message.
The two hydraulic valves are preferably implemented as economical slide valves, which normally exhibit a certain leakage, depending on the temperature of the hydraulic fluid and the pressure differential. If, for instance, the first hydraulic valve should lose power and switch back due to a cable breakage or the like during travel, i.e., with a disengaged parking lock, it is possible for the piston chamber of the actuating piston to be slowly emptied back into the sump via internal leakage of the second hydraulic valve. Specifically to prevent this, a preferred refinement of the invention provides that the piston chamber of the actuating piston be connected to the pressure source via an additional valve arrangement.
A pressure-maintaining check valve, which prevents a backflow from the piston chamber to the pressure source, and a throttle point are expediently arranged in series in a connection line linking the piston chamber to the pressure source. Thus, the piston chamber of the actuating piston can also be supplied directly from the pressure source via the pressure-maintaining check valve and the throttle point when the parking lock is completely releasedxe2x80x94that is, when the piston chamber is under pressure, the actuating piston is moved into the disengaged position and the leakage compensation valve is openedxe2x80x94so that pressure is maintained even in case of leaks. In case of a pressure drop during travel, the pressure-maintaining check valve prevents the piston chamber from being emptied by a backflow via the connection line to the sump (due to leakage of the first hydraulic valve). For the case where the actuating piston is to be brought into its engaged position by the hydraulic valves connecting the piston chamber to the sump, the throttle point limits the inflow to the piston chamber and thus permits a sufficient fluid drainage via the hydraulic valves, so that the actuating piston can assume its engaged position and remain in this position.
It is of particular advantage to arrange a controllable leakage-compensation valve in the connection line linking the piston chamber to the pressure source, through which valve a fluid flow from the pressure source to the piston chamber can be controlled. The leakage-compensation valve is preferably a check valve pressed by a restoring spring into the closed position. It is expedient to couple the leakage-compensation valve via a mechanical connecting member to the actuating piston so that it is always open whenever the actuating piston assumes its disengaged position. If the actuating piston is in the non-pressurized engaged position, then the leakage-compensation valve is not opened by the mechanical connecting member, but is instead closed due to system pressure or spring-loading. An unintentional disengagement of the parking lock by direct fluid supply from the pressure source is thus out of the question in this piston position.
It is particularly advantageous to connect the piston chamber of the actuating piston to the sump via a drain valve, which is opened without pressure by spring force. When the parking lock is set, that is, when the actuating piston is not pressurized, a certain amount of leakage fluid can be removed via this drain valve. This is of particular importance if the regular connection between the actuating piston and the sump via the hydraulic valves is closed off due to faulty power supply to the first hydraulic valve (e.g., short circuit to 12 V). Then, due to this amount of leakage fluid, an accumulated pressure could build up in the piston chamber of the hydraulic cylinder which could lead to an undesired disengagement of the parking lock in this fault situation. In the regular disengagement of the parking lock, the drain valve is immediately closed by the flow force of the fluid stream released through the hydraulic valves. The opening pressure of the drain valve is expediently chosen to be higher than the opening pressure of the check valve in the second connection line so that, after shutting of the two hydraulic valves, when the pressure in the piston chamber therefore drops, the drain valve is actually opened and not kept closed by the slight residual pressure (e.g., 0.2 bar) in the pressure chamber corresponding to the spring force of the aforesaid check valve.
The locking device preferably features a detent pawl seated in the transmission housing which can be brought into engagement with a gearwheel firmly connected to the vehicle axle. The detent pawl is connected to the actuation drive element via mechanical connecting element. The tooth geometry is preferably designed to be repellent so that, even under maximum loads, the detent pawl goes securely out of engagement when the actuation is terminated.
For the case where the vehicle must be towed in case of a failure of the on-board electrical or hydraulic systems, the parking lock must be released. To this end, a preferred refinement of the invention provides for the arrangement, parallel to the above-described components of the control device, in particular, the electro-hydraulic actuation, of a mechanical emergency actuation device for disengaging and re-engaging the parking lock. When the mechanical emergency actuation device is operated, the locking device of the parking lock is disengaged against the retaining force of a parking lock spring and fixed in this position.
It is of particular advantage here to link the locking device optionally to a clutch pedal such that, by operating the clutch pedal, the locking device assumes its disengaged position. The linkage can be accomplished by detachable connecting elements.
Furthermore, the mechanical emergency actuation device is constructed such that the normal movements of the mechanical park lock actuation do not cause any movement of the mechanical emergency actuation device. This can be assured by the appropriate lost motion or freewheel functions.
According to a preferred embodiment of the invention, at least one electrical controller is provided which issues electrical control signals to the hydraulic valves for engaging (no current flow) and disengaging (current flow) the parking lock. This expediently involves a transmission controller that executes the functions of the invention. The command for engaging and disengaging preferably is initiated directly by the vehicle user or comes from a transducer of the operating lever or from another measurement transducer, for instance, an rpm sensor or a measurement transducer of particularly safety-relevant measured parameters, which are evaluated by the controller.
It is also advantageous to provide a transducer, in particular, a pressure sensor, which directly or indirectly detects the position of the locking device and communicates it to the controller, so that an acknowledgment of the actual parking lock position is available at all times.
An advantageous configuration of the invention provides a main, or transmission, controller and a backup, or parking lock, controller, which are independently supplied with power and communicate with one another. The command for engaging or disengaging the parking lock is, on the one hand, sent directly from the main controller to the first hydraulic valve and, on the other, via the backup controller to the second hydraulic valve. Preferably, both controllers independently receive rpm signals from the vehicle""s drive unit.
This arrangement offers redundancy. With it, it is possible to prevent a defective controller or a defective sensor from causing an unintended setting of the parking lock above a preset travel velocity or an unintended disengagement at rest with the motor running (supply pressure!). The direct power supply to the backup controller (separate connection to the vehicle battery) assures that turning off the ignition during travel does not cause automatic setting of the parking lock. A wake-up signal can also be generated by a line from the ignition lock to the backup controller. The two controllers are connected together via communications lines which serve for mutual monitoring.
Preferably, at least one sensor or switching element for detecting the position of an emergency actuation device, such as a clutch pedal is provided, the signals of which are detected and evaluated by the controller.
The design of the invention uses existing components of the parking lock contained in the transmission (gear, pawl, camshaft) and can be added on from the outside as an electro-hydraulic actuation element, so that automated operation of an existing transmission can be retrofitted. The capability for operation via auxiliary power is a considerable improvement of comfort and also makes it possible to integrate the parking lock functions into modern operating elements (joystick, armrest controls, and so on). The design is safe in operation in case of failure of the auxiliary hydraulic power and in case of various interruptions/short circuits and in case of faulty operation (setting the parking lock or turning off the ignition during travel). Even if there is a faulty power supply to one of the two hydraulic valves, the selected operational state (in this case, park) is safely preserved. The hydraulic circuit is constructed of simple, commercially available and reliable components.
Because of the electronic control of parking lock actuation, additional functions can be implemented, in addition to the execution of the driver""s instructions:
automatic setting of the parking lock at rest if the engine is turned off or, in the case of infinitely variable transmissions, if the state xe2x80x9cnon-positively locked stoppagexe2x80x9d exceeds a certain length of time;
prevention of setting the parking lock at speeds above a predetermined value (e.g., 1 km/h), even if the driver calls for this;
automatic setting of the parking lock when the vehicle comes to a stop, in case of transmission defects;
continuous plausibility querying and issuance of error messages.
The invention, as well as additional advantages and advantageous refinements and configurations of the invention, will be described and explained in greater detail on the basis of the drawing, which shows an embodiment of the invention. In the sole figure, the functional plan of a control device according to the invention with hydraulic and electrical control loops is schematically illustrated.